Method of transmitting and receiving acknowledgment signal in a wireless communication system

ABSTRACT

A method of receiving an acknowledgement (ACK) signal from at least one access terminal (AT) in a wireless communication system is disclosed. More specifically, the method includes transmitting at least one packet via a packet data channel from an access network (AN), receiving at least one ACK signal from the at least one AT using same channelization resources, wherein each AT is assigned a code specific to each AT, and identifying the ACK signal corresponding to the transmitted packet from the received at least one ACK signal.

This application claims the benefit of U.S Provisional Application No.60/794,944, filed on Apr. 25, 2006, which is hereby incorporated byreference, and claims the benefit of U.S. Provisional Application No.60/885,388, filed on Jan. 17, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of transmitting and receivinga signal, and more particularly, to a method of transmitting andreceiving an acknowledgment signal in a wireless communication system.

2. Discussion of the Related Art

In the world of cellular telecommunications, those skilled in the artoften use the terms 1G, 2G, and 3G. The terms refer to the generation ofTee cellular technology used. 1G refers to the first generation, 2G tothe second generation, and 3G to the third generation.

1G refers to the analog phone system, known as an AMPS (Advanced MobilePhone Service) phone systems. 2G is commonly used to refer to thedigital cellular systems that are prevalent throughout the world, andinclude CDMAOne, Global System for Mobile communications (GSM), and TimeDivision Multiple Access (TDMA). 2G systems can support a greater numberof users in a dense area than can 1G systems.

3G commonly refers to the digital cellular systems currently beingdeployed. These 3G communication systems are conceptually similar toeach other with some significant differences.

In a wireless communication system, it is important to devise schemesand techniques that increase the information rate and improve therobustness of a communication system under the harsh conditions of thewireless environment. To combat less-than-ideal communication conditionsand/or to improve communication, various methods, including reducingtransmission of unnecessary data, can be used to free up resources aswell as promote more effective and efficient transmission.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method oftransmitting and receiving an acknowledgment signal in a wirelesscommunication system that substantially obviates one or more problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of receivingan acknowledgement (ACK) signal from at least one access terminal (AT)in a wireless communication system.

Another object of the present invention is to provide a method oftransmitting an acknowledgement (ACK) signal from at least one accessterminal (AT) in a wireless communication system.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of receiving an acknowledgement (ACK) signal from at least oneaccess terminal (AT) in a wireless communication system includestransmitting at least one packet via a packet data channel from anaccess network (AN), receiving at least one ACK signal from the at leastone AT using same channelization resources, wherein each AT is assigneda code specific to each AT, and identifying the ACK signal correspondingto the transmitted packet from the received at least one ACK signal.

In another aspect of the present invention, a method of transmitting anacknowledgement (ACK) signal from at least one access terminal (AT) in awireless communication system includes receiving at least one packet viaa packet data channel from an access network (AN), and transmitting anAT-specific ACK signal to the AN using same channelization resourcesshared by other ATs for transmitting respective ACK signals.

In a further aspect of the present invention, a method of receiving anacknowledgement (ACK) signal from at least one access terminal (AT) in awireless communication system includes transmitting a multi-user packet(MUP) including a preamble and a plurality of packets arranged insequential order which indicates an AT-specific code that corresponds toeach AT, and receiving the ACK signal from the each AT, wherein the eachAT corresponds to the AT-specific code.

Yet, in another aspect of the present invention, a method oftransmitting an acknowledgement (ACK) signal from at least one accessterminal (AT) in a wireless communication system includes receiving amulti-user packet (MUP) including a preamble and a plurality of packetsarranged in sequential order which indicates an AT-specific code, andtransmitting the ACK signal by the AT after decoding a packet from theplurality of packets which corresponds to the AT-specific code.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 is an exemplary diagram illustrating possible collision of ACKssent from multiple ATs via shared channel;

FIG. 2 is an exemplary diagram illustrating different starting pointsfor each sequence; and

FIG. 3 is an exemplary diagram illustrating a plurality of ATs usingdifferent codes in a MUP.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The ultra mobile broadband (UMB) combines various aspects of codedivision multiple access (CDMA), time division multiplexing (TDM),LS-OFDM, orthogonal frequency division multiplexing (OFDM), and OFDMaccess (OFDMA) into a single air interface using sophisticated controland signaling mechanisms and advanced antenna techniques (e.g., multipleinput multiple output (MIMO) and space division multiple access (SDMA)).As a result performance can be enhanced.

Among various advantageous, the UMB efficiently supports centralizedaccess network. In the UMB, an access terminal (AT) maintains separateprotocol stack for each base station (BS) or access network (AN) in theactive set. The BSs are connected by an inter-AN interface. The inter-ANinterface supports tunneling of layer 2 and/or layer 3 packets, sessiontransfer, and other functions such as paging and neighbor discovery.However, the inter-AN interface need not support one BS/AN in control ofconnection state at another AN, interpretation/translation of tunneledpackets by serving AN, or transfer of RoHC/Connection/RLP state. Inaddition, each cell can be a separate AN/BS.

Further, each BS in the active set uses a separate data route. In otherwords, there is no need to transfer RLP and header compression statebetween BSs. In addition, traffic flow between the BS and the AT can betunneled through the serving BS. Here, this supports fast and seamlessre-pointing between cells/sectors.

Each BS in the active set can use a separate personality. That is, therecan be seamless handoff across air interface revision boundaries.Moreover, signaling message of protocols between a BS and an AT can betunneled through the serving BS. Here, the BS which acts as a tunnelneed not interpret the tunneled messages. Moreover, there is no protocolconversion between BSs.

Regarding connection maintenance, the BS does not have to maintainconnection state of other BSs in the active set, which means that the BSdoes not need to synchronize connection state across BSs.

In the UMB, reverse link allows manycast. That is, the AT can send apacet once over the air and address it to multiple BSs or ANs. Moreover,UMB layering reduces the number of protocols in the data path.

In a wireless communication system, such as the UMB, various design ofhigh speed packet air interfaces using automatic request (ARQ) or ahybrid ARQ (H-ARQ) over the forward link (FL) and reverse link (RL) canbe implemented With respect to the FL, after a base station (BS) sends apacket on the FL to an access terminal (AT), the AT can respond with apositive acknowledgement (ACK) or a negative acknowledgement (NAK)indicating whether the packet is successfully received or not. The ACKor NAK is typically indicated using a RL ACK channel.

Hereinafter, the BS can also be referred to as an access network, anode, Node B, serving BS, and a network. Furthermore, the AT can also bereferred to as a mobile station, a terminal, mobile subscriber station,and a terminal station. The discussions to follow are applicable tomulti-user packet (MUP).

In 1xEV-DO (1x Evolution Data Optimized) system, the ACK/NAK can be sentvia a dedicated channel. That is, the ACK and/or NAK signal is sent on adedicated RL ACK and/or NAK channel.

With continuing developments in the systems features and capabilities,such as the UMB, with respect to the RL ACK channel, it is possible touse a shared (or common) ACK channel among RL terminals. The AT can usea particular resource (e.g., frequency tones) reserved for the ACK for aparticular FL packet channel. For example, if there is only one ATscheduled at a time in a time division multiple access (TDMA) fashion,then the BS of the serving cell/sector can expect to receive at most oneRL ACK from the scheduled AT. Here, this ACK is sent over the reservedroute.

Furthermore, assume that there are two (2) ATs, for example. If thesetwo (2) ATs can be scheduled simultaneously, then two (2) common ACKchannels can be used to send ACK to each of the two (2) corresponding FLpackets distinctly. That is, the two (2) ACK channels could use two (2)distinct set of frequency tones to provide orthogonality and nocross-interference.

However, there can be difficulties associated with the shared or commonRL ACK channel. More specifically, since the resources are shared,collisions can occur with ACKs sent from multiple ATs. FIG. 1 is anexemplary diagram illustrating possible collision of ACKs sent frommultiple ATs via shared channel. As illustrated, ACK sent via anacknowledgement channel (ACKCH) from each AT (i.e., AT₁ and AT₂) aresent on ACKCH₁ or put differently, reverse-ACKCH₁ (R-ACKCH₁). Since theshared ACKCH serves ACK sent to two (2) different sectors, collision canoccur between the ACK sent from AT₁ and the ACK sent from AT₂.

As discussed, the shared RL ACK channel can experience collision. Thatis, it is possible that another AT may mistakenly determine that it isbeing scheduled. Consequently, both the “mistaken” AT(s) and “actuallyscheduled” AT can transmit on the same common ACK channel and, collide.In such a situation, the receiver at the BS would greatly reduce thereliability of the ACK channel from the intended AT. Here, there is apossibility of interference from other ATs elsewhere transmitting insome or all of the same tones.

To address the possible collision that can take place in the shared RLACK channel by a mistaken AT, a physical layer waveform of the ACKsignal (at the AT transmitter) can be encoded with a unique and/orAT-specific code. For example, the ACK signal can be encoded with ascrambling code unique to the AT. Here, the AT-specific code can also bereferred to as a medium access control (MAC) identification (ID).Moreover, the AT-specific code can be defined in the preamble to includethe position of the AT in a multi-user packet (MUP). In addition, theAT-specific code can be a scrambling code.

In a 1xEV-DO system, the long pseudo noise (PN) sequence can be used.That is, the offset for each AT can be changed so as to make each ATunique and distinguishable. This can be made possible since the sequenceis long. For example, FIG. 2 is an exemplary diagram illustratingdifferent starting points for each sequence. Referring to FIG. 2,different offset is provided. Sequence 1 starts at point 1, Sequence 2starts at a different point further along in the clock-wise direction,and so on. This way, as discussed, each sequence can be made unique anddistinguishable.

In addition, other sequences can be used as well, such as Walsh codeswhich could be assigned at call start up. The BS scheduler knows whichAT has been scheduled and the scrambling code it is expecting. Hence,when the received scrambling code differs, then the scheduler knows thatthere has been an error. Even if there are two more signals sending anACK, it may be possible to detect the desired AT's ACK response giventhe encoding.

Here, since the BS scheduler knows which user was scheduled, thereceiver would know the physical layer waveform it can expect tosee/receive, especially since this physical layer waveform is ATspecific. Further, by encoding ACK signals, this can also allow formultiplexing of ACK signals to provide greater frequency diversity. Thisassumes the availability of one or more tones for ACK signaling.

If the ACK is sent in an AT-specific environment, interference and/orcollision is not likely to occur and is absent of orthogonality.However, with sector-specific system, interferences and/or collisionscan occur between sectors (as illustrated with respect to FIG. 1). Here,however, interferences and/or collisions do not take place within thesector, only between sectors.

As such, in the shared channel environment, it is possible that anotherAT (AT_B) from a different sector (Sector B) may use the same RLresources as that for the AT of interest (AT_A) in the sector ofinterest (Sector A). In this case, as above, the ACK channel of AT_A andthat for AT_B can collide when they are transmitted at the same timeover the same resources. For example, the ATs from different sectors maytransmit using the same RL orthogonal frequency division multiplexing(OFDM) resources resulting in collision.

To address the possible collision that can take place in the shared RLACK channel due to sharing of the same RL resources from ATs ofdifferent cell/sectors, a physical layer frame of the ACK signal can beencoded using a sector-specific scrambling code.

For example, in Ultra-Mobile Broadband (UMB), each AT can be assignedtwo (2) discrete Fourier transform (DFT) codes where the length of eachis 16. The ACK can be sent by sending energy on one of the DFT code.Here, nothing is sent over the other DFT code. Moreover, the NAK can besent by having no energy sent on either DFT code.

A problem that can arise here is that the same DFT codes and OFDMresources are re-used in adjacent sectors and, hence, collisions canoccur which become more acute when the interfering AT is closer to thesector-boundary region (e.g., poor geometry AT). In this case, each ATin a particular sector (e.g. Sector A) can use a sector-specificscrambling code to randomize the mapping of the DFT code to the OFDMsub-carriers. This randomized mapping can be achieved by using asector-specific interleaver and/or an interleaver controlled by asector-specific scrambling code.

Further to resolving a collision problem, the channelization resourcesof an ACKCH can be made variable. Typically, the channelizationresources of the ACKCH are fixed regardless of the data rate of itscorresponding packet data channel (PDCH). Instead of fixing the amountof resources assigned to an ACKCH, the amount of resources assigned toan ACKCH can be made variable according to the data rate of the PDCH.The benefit of this approach is that as the PDCH data rate increases,the value of having a more reliable ACKCH increases. An ACKCH using moreresources can achieve greater frequency diversity and, hence, greaterreliability.

In addition, making variable the resources assigned to the ACKCH canreduce the likelihood of ACKCH decoding failure which introduces otherproblems such as unnecessary re-transmissions (when an ACK is decodedincorrectly as a NAK) and/or the absence of a needed re-transmission(when a NAK is decoded incorrectly as an ACK).

Further to resolving the collision problem, instead of using the PDCHdata rate, the PDCH data transmission format and/or number ofchannelization resources can be used (e.g., channelization codes in CDMAor tiles in OFDM used by the PDCH).

With respect to the UMB, an AT is restricted to using one R-ACKCHresource unit consisting of two DFT codes over four sub-tiles (whereeach sub-tile is located typically as far as apart as possible in thefrequency domain to ensure frequency diversity). If there are leftoverR-ACKCH resources, the ATs can use more than one R-ACKCH resource.

The structure of the UMB includes a preamble and 25 physical frames.There are eight (8) OFDM symbols per preamble and physical frame. As forthe preamble, first 5 OFDM symbols are carried by the preamble.

In addition, sector-specific hopping of the R-ACKCH and/or sub-tilesamong different OFDM resources can take place. For example, there are aset of ACKCH's (16 DFT codes) hop in a sector-specific pseudo-randomizedfashion from one frame to another frame.

Further, scrambling of the sub-tile locations with each tile can takeplace. Currently, they are set to the bottom half of a tile. Have themrandomly assigned within the tile to minimize collisions.

In addition, multi-user packets (MUPs) is an existing air-interfacefeature in 1xEV-DO which allows multiple ATs to be scheduled using acommon transmission format and shared resources (time, frequency and/orspace). With MUP, the ATs, which successfully decode an MUP packet, cansend an ACK over a dedicated channel and not over the shared channel.Otherwise, it sends nothing. With respect to using the shared ACKchannel, as discussed, it is possible for multiple ATs to transmit anACK over the shared ACK channel and, hence, collision can occur.

To address possible difficulties associated with collision that can takeplace with respect to MUP, the sequencing information implicit in a MUPcan be used. More specifically, the ATs in a MUP can be sequenced. Forexample, in 1xEV-DO, the header and information bits for each user areordered in a sequential fashion such that up to eight (8) ATs can beordered. The ACK channel can be modulated one of eight orthogonal (ornon-orthogonal but distinct) codes. For example, the eight length-8Walsh codes can be mapped to indicate the ACK of each of the up to eightATs.

FIG. 3 is an exemplary diagram illustrating a plurality of ATs usingdifferent codes in a MUP. Referring to FIG. 3, each AT uses a prescribedcode which is different from the prescribed code used by other ATs.Here, AT_A uses scrambling code sequence 1 while AT_B uses scramblingcode sequence 2, and so on.

Further, the encoding can be performed in the time domain, frequencydomain, or some combination of the two. In the time domain-onlysolution, there would need to be at least eight instances of the ACK bittransmission.

Consider the above example requiring eight (8) ACKs. In thefrequency-domain-only solution, there would need to be at least eighttones to allow for multi-code CDMA. In the combined time and frequencysolution, some mixture of the two can be used. For example, if there aretwo transmission instants (one repetition), then at least 4 frequencytones would be needed.

The difficulties discussed associated with the shared RL ACK channel canalso be applied to the RL for scheduled ATs.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of receiving an acknowledgement(ACK)/negative acknowledgement (NAK) signal at a base station (BS) in awireless communication system using orthogonal frequency tones, themethod comprising: transmitting, by the BS, a data packet to a mobilestation; receiving, by the BS, a first ACK/NAK signal via a first set oforthogonal frequency tones from the mobile station; and receiving, bythe BS, a second ACK/NAK signal via a second set of orthogonal frequencytones from the mobile station, wherein the first ACK/NAK signal and thesecond ACK/NAK signal carry the same information and correspond to thedata packet, wherein the first set of orthogonal frequency tones and thesecond set of orthogonal frequency tones are shared between a pluralityof mobile stations for ACK/NAK signal transmission by using a pluralityof sequences corresponding to the plurality of mobile stations, andwherein the first set of orthogonal frequency tones is different fromthe second set of orthogonal frequency tones over two transmissioninstants.
 2. The method of claim 1, wherein the plurality of sequencesare a plurality of scrambling sequences.
 3. The method of claim 2,wherein the plurality of scrambling sequences are pseudo noise sequencecodes.
 4. The method of claim 1, wherein the plurality of sequences aregenerated from an origin.
 5. A method of transmitting an acknowledgement(ACK)/negative acknowledgment (NAK) signal at a mobile station in awireless communication system using orthogonal frequency tones, themethod comprising: receiving, by the mobile station, a data packet;transmitting, by the mobile station, a first ACK/NAK signal via a firstset of orthogonal frequency tones; and transmitting, by the mobilestation, a second ACK/NAK signal via a second set of orthogonalfrequency tones, wherein the first ACK/NAK signal and the second ACK/NAKsignal carry the same information and correspond to the data packet,wherein the first set of orthogonal frequency tones and the second setof orthogonal frequency tones are shared between a plurality of mobilestations for ACK/NAK signal transmission by using a plurality ofsequences corresponding to the plurality of mobile stations, and whereinthe first set of orthogonal frequency tones is different from the secondset of orthogonal frequency tones over two transmission instants.
 6. Themethod of claim 5, wherein the plurality of sequences are a plurality ofscrambling sequences.
 7. The method of claim 6, wherein the plurality ofscrambling sequences are pseudo noise sequence codes.
 8. The method ofclaim 5, wherein the plurality of sequences are generated from anorigin.